The present invention relates to a regeneration system for a particulate trap, and in particular to a system for controlling the flow rate of air introduced upon the regeneration (combustion) of a particulate trap (hereinafter abbreviated as trap) provided in the exhaust pipe of an engine.
In prior art regeneration systems for a trap comprising a regenerating thermal source such as an electric heater or a gas oil burner, the flow rate of regenerating air into/from the regenerating thermal source is controlled to optimize the trap temperature upon the regeneration, as disclosed e.g. in Japanese Patent Application laid-open Nos. 60-19908 and 60-50211.
In order to maintain the trap temperature upon the regeneration (i.e., the regeneration temperature) at an optimum value, such systems detect the temperature of the regenerating thermal source to fix the thermal output (quantity of heat), and also control the flow rate of the regenerating air, so that a flow rate with a fixed weight (oxygen weight content) suitable for the regeneration may be supplied for the trap at all times, even though atmospheric pressure and temperature vary.
On the other hand, the average temperature of the trap upon regeneration is determined from the trap inner temperature at the time of initiation of the regeneration in view of the fact that 1 since the weight of particulates accumulated in the trap at which the regeneration time has come, is considered to be almost constant, the heat value (calorific value) during the regeneration is also constant, and 2 the heat capacity of the trap during the regeneration is constant.
However, such systems disclosed in the above-noted publications control the flow rate of the regenerating air regardless of the trap temperature (heat capacity) at the initiation of the regeneration, so that the trap temperature at the initiation of the regeneration varies the trap temperature upon the regeneration.
Namely, for example, in the event the temperature of the trap is high due to a high loaded engine condition or hot atmosphere immediately before the regeneration process, the average temperature of the trap upon the regeneration becomes so excessively high that the trap may be melted, while in the event the temperature of the trap is low due to a low loaded engine condition or cold atmosphere, the average temperature of the trap is so low that a suitable regeneration for the accumulated particulates can not be maintained.